In today's vehicles, map data Dmap are used in many areas of application. One such area is for navigation by means of a positioning system, e.g. a GPS (global positioning system). Another such area is for estimation of running resistance for a vehicle. In such estimations, map data related to road gradients α are very important. Another such area is in today's economical cruise controls which take account inter alia of the running resistance, which itself depends inter alia on the road gradient α. Another such area is various systems for automatic gearchanging, in which gear choice is for example based on road gradient α. Map data related to road curvature are also used by various systems.
Today's traditional cruise controls maintain a constant reference speed vref which corresponds to the speed vset chosen by the driver. The value of the reference speed vref is only altered when the driver adjusts the set speed vset while driving. Certain economical cruise controls, e.g. Scania's Ecocruise, try to estimate a current running resistance and also have knowledge of the historical running resistance.
An experienced driver of a vehicle without cruise control can reduce fuel consumption by adapting his/her driving to the characteristics of the road ahead so that unnecessary braking and/or fuel-consuming acceleration can be avoided. A further development of the aforesaid economical cruise controls tries to mimic the experienced driver's adaptive driving on the basis of knowledge of the road ahead so that fuel consumption can be kept as low as possible, since this very greatly affects profitability for an owner of the vehicle, e.g. a haulage company or the like.
An example of such a further development of an economical cruise control is a “Look Ahead” cruise control (LACC), i.e. a strategic cruise control which uses knowledge of road sections ahead, i.e. knowledge of the nature of the road ahead, to determine the reference speed vref. Here the reference speed vref is therefore allowed, within a certain speed range, to differ from the set speed vset chosen by the driver, in order to run the vehicle in a way which saves more fuel.
Knowledge of the road section ahead may for example comprise prevailing topography, road curvature, traffic situation, roadworks, traffic density, state of road, speed limits on the road section ahead, and traffic signs beside the road. This knowledge may for example be obtained from location information, e.g. GPS (global positioning system) information, map data Dmap and/or topographical map data, weather reports, weather measurements, information communicated between different vehicles and information communicated by radio. These different types of knowledge may be used in various ways. For example, knowledge of a speed limit on the road ahead may be used to achieve fuel efficiency by lowering the vehicle's speed before the lower speed zone is reached. Similarly, knowledge of a road sign conveying information about, for example, a roundabout or intersection ahead may also be used for fuel efficiency by braking before reaching the roundabout or intersection.
With an intelligent cruise control which takes account of topography ahead, i.e. a Look Ahead cruise control, the vehicle's reference speed vref can therefore be optimised for different types of road, engine performance and train weight in order to achieve fuel saving if this is prioritised. A more powerful vehicle can also be achieved if this is optimised, as in the “power mode” application. A higher mean speed can also be achieved without increasing the fuel consumption.
An economical cruise control may for example predict the vehicle's speed along a horizon of any suitable length, e.g. about 1-2 km. The vehicle's future speed along the horizon may be predicted in various ways, such as driving with a traditional cruise control with a reference speed vref which is the same as the set speed vset, or varying the reference speed vref relative to the set speed vset.
A Look Ahead cruise control (LACC) does for example allow the reference speed vref to be raised, before an upgrade, to above the set speed vset, since the vehicle will presumably lose speed on the upgrade owing to high train weight relative to engine performance. Similarly, the LACC allows the reference speed vref to drop to below the set speed vset before a downgrade on which the vehicle will presumably be accelerated by its train weight. The concept here is that it is better from a fuel economy perspective to take advantage of the vehicle's acceleration by its own weight downhill than to initially accelerate before the downgrade and then brake on the downgrade. The LACC can thus reduce fuel consumption without greatly affecting journey time.
There are also cruise controls which use a current running resistance as a basis for deciding how the vehicle's speed should vary. In such cruise controls, the reference speed vref can be allowed to deviate from the set speed vset on the basis of at least one characteristic of the running resistance, e.g. its magnitude and/or pattern over time.
Examples of known systems for presenting map data are found in e.g. EP1562021, EP1530026, DE102009018073 and DE102008012697.